fetus should have been sought either in the mother's or in 

 the father's body. 



The ovary of the mother contains parts, such as the 

 ova, which give the beginning to a new individual. It was 

 possible to assume preformation in the ova. From the other 

 side, after the invention of the magnifying lens, observers 

 found in the male an enormous number of small, spontaneously 

 moving animals, i.e. live bodies. This observation was 

 extremely welcomed by the supporters of preformation. The 

 fact of the enormous quantity of these bodies in the male 

 testicles was difficult to explain. Defenders of preforma- 

 tion believed that the moment of fertilization millions of 

 the male bodies (called cercaria) violently fight with each 

 other, until those lucky few live conquerors penetrate into 

 the vesicle of the female ovary. It is only a pity, Baer 

 speaks ironically, that these bodies do not have jaws to 

 bite each other. In general they do not have even the most 

 remote similarity to the higher animals, but consist only 

 of a small head and a long tapering tail. 



"After a brief flourishing," Baer continued, "this 

 hypothesis, like the hypothesis of preformation in the egg, 

 was forgotten and faded throughout half a century. Only 

 recently two very accurate observers, Prevost and Dumas, 

 have revived it as a result of a thorough investigation of 

 the testicular beasts." About the cercaria, Baer cited the 

 words of Prevost and Dumas that "not the complete hen or cow 

 is formed from the cercaria, but only the nervous system, 

 while the others grow from the female reproductive material" 

 (II Id, 5). Actually, Baer continued, the cephalic brain, 

 in combination with the spinal cord, has a form somewhat 

 similar to the cercaria magnified a million times" (II Id, 6) 

 The first part of Prevost 's and Dumas 's work^ was received, 

 according to Baer, with complete confidence. However, when 



2. J(ohn) L(ouis) Prevost and J(ean-Baptiste) Dumas, 

 NOUVELLE THEORIE DE LA GENERATION (New theory 

 of generation) (Paris, 1824). ANNALES DES 

 SCIENCES NATURELLES, 1 (1824), pp. 1-29, 

 167-187, 274-292. 



368 



